Circular saw blades are normally driven by rotating shafts connected to motors. In many applications, the rotating cutting blades have circular holes through the center for acceptance of a circular drive shaft. The shafts often have a smaller diameter mounting portion which extends from a larger primary portion of the drive shaft to form a shoulder. The blades are typically pressed over the smaller diameter mounting portion until they are stopped against the shoulder formed by the main drive portion of the shaft. The blade is then locked onto the shaft by clamping it between the shoulder on the main portion of the drive shaft and either a threaded locking nut which is threaded onto the end of the small diameter mounting portion or a bolt threaded into a threaded hole in the end of the shaft. The friction from the clamping force prevents the blade from rotating with the shaft.
Often times, material is allowed to enter the hole in which the clamping bolt is threaded. This prevents the bolt from being tightened sufficiently into the threaded hole in the shaft. When this occurs, there is an insufficient clamping force to hold the rotating cutting blade against the shoulder, and because the mounting is circular, the blade may slip. When the blade slips with respect to the shaft, the blade speed often decreases rapidly, causing spalling or chipping of the concrete surface adjacent groove being cut.
In order to remedy this problem, non-circular arbor sleeves, or cutting blade mounting members, can be attached to the drive shafts. The arbor sleeves are normally securely mounted to the drive shaft, so they do not rotate. For example they can be clamped, welded, pinned to the shaft, keyed, or held by set screws. A surface of the arbor sleeve is used as the surface upon which the rotating cutting blade is then mounted. The cutting blade is configured to have a mounting hole of the same size and shape of the arbor to allow it to be positioned over the arbor to be driven by the motor drive shaft.
Arbor sleeves are normally square or a circular shaft with symmetric flutes, although they may have other symmetric configurations. The shape of the arbor sleeve is symmetrical on its outer surface, in order that the cutting blade may be easily mounted on it without much alignment effort. When a non-circular arbor sleeve is employed, the cutting blade may not slip, as the hole of the blade and the outside of the arbor sleeve have sides which contact one another.
Alternatively, the drive shaft can be configured to have a symmetric non-circular end, and the cutting blade configured to have a correspondingly shaped hole through which the arbor can be inserted. While it is possible to have the blade mounting area of the drive shaft, or arbor, itself be machined into the desired shape, sleeves are more easily machined at lower cost.
Because the arbors or arbor sleeves are symmetrical in shape, the cutting blade may be mounted so that either side of the cutting blade faces the saw. Normally, the person installing the saw will orientate the cutting blade so the teeth on the blade are in the correct orientation relative to the direction the saw is to travel during cutting. For wood cutting saw, the saw teeth orientation is apparent, and the blade can be easily orientated to rotate in the correct direction relative to the direction that the saw will travel during cutting.
With concrete cutting saws, however, the teeth do not have a readily apparent directional orientation. Concrete cutting saw blades are made with diamond impregnated cutting segments that are symmetrically shaped. When used to cut hardened concrete and when water lubricated, the blades can be used in either orientation, or with either side of the blade toward the saw when the saw is traveling in the same direction. Thus the orientation of the water lubricated blade on the saw does not matter for cured, hardened concrete.
When the same blade is used to cut wet or very green concrete without water lubrication, however, the blade orientation is important. The cutting segments are formed by having harder cutting media, such as diamond chips or tungsten carbide particles, being placed in a softer support or binding matrix, such as bronze or other softer metals. The cutting segments are either formed on the metal support disk, or formed separately and then bonded to the support disk. After the cutting segments are on the disk, the cutting segments are dressed by slightly abrading the cutting segments to remove enough of the binding matrix to expose the cutting particles. This dressing typically leaves one side of the cutting particles exposed while the opposite side has a trail of the softer binding matrix extending from the cutting particle (FIG. 10). If the cutting blade is rotated so that the exposed side of the particles face the direction of the blade rotation, the blade cuts well. If, however, the blade is orientated the other way so that the exposed portion of the cutting particles face away from the direction of the blade rotation, then the cutting blade will not cut well because only the binding material and not the cutting particles contact the concrete. This will also occur if the blade is not dressed sufficiently and the cutting particles are not exposed adequately before cutting. When the blade is mismounted or is insufficiently dressed, chattering of the blade and spalling and/or chipping of the concrete occurs when the blade is used to cut the concrete. Further, because the blade is not water lubricated when cutting wet or very green concrete, the friction created between the concrete and the binding material causes extreme heat build-up, causing the blade to warp, which in turn damages the surface of the concrete surrounding the cutting blade. In some cases, the heat build-up combined with the chattering of the warped blade will cause the cutting segments to detach from the blade. This situation is dangerous, as the cutting segments may be propelled into the user and cause injury, or be propelled into and damage the saw.
Previously, cutting blades used to cut wet concrete were labeled with notices such as "this side out," to insure correct orientation of the blade on the saw. That labeling, however, is not always effective. There is thus needed a way to insure correct orientation of a circular concrete cutting saw blade on the saw, and a way to guard against rotation of the saw blade relative to the drive shaft.